Year Observations     Objects
1950            2          1 
1951            6          3 
1953            4          2 
1954            2          1 
1955            4          2 
1956            2          1 
1960            6          3 
1974            2          1 
1975            2          1 
1976            8          4 
1977            2          1 
1978            8          3 
1981            4          2 
1982           12          6 
1983            8          4 
1984            2          1 
1985            8          4 
1986            4          2 
1987            2          1 
1988           38         18 
1990           32         14 
1991          532        200 
1992          936        367 
1993         1681        614 
1994         2348        847 
1995         4454       1537 
1996         3611       1268 
1997         2350        801 
1998        23402       9861 
1999        14706       5644 
2000        41052      17053 
2001        42187      16471 
2002        33553      14971 
2003        62709      25986 
2004        49344      18944 
2005        88640      27196 
2006       114850      36591 
2007       210318      64292 
2008       131757      37401 
2009       107302      30098 
2010       124829      34587 
2011       188033      51990 
2012       174783      48332 
2013       272017      77074 
2014       673585     171818 
2015       771787     205019 
2016       550333     148155 
2017       472366     134942 
2018       405668     113991 
2019       807002     197448 
2020       719737     184853 
2021       936111     225300 
2022       710106     203194 
2023       565553     161799